BOOM is widely used in the beer pong community for pretty much any reason. It is shouted as loud as possible so that everyone is aware of what just happened and are now compelled to BOOM as well. Can be used in conjuction with LFG

A word used to express satisfaction. or after something that has happened (generally after a good thing). Also if something is done right multiple people will say boom. If Boom is said then sometimes people may copy and say it after.